1. Field of the Invention
The present invention relates to an aircraft and a fuel venting system therefor, in particular, but not exclusively large, multi-engined aircraft with anhedral wings.
2. Description of the Related Art
Large, multi-engined aircraft are often provided with fuel tanks defined by internal spaces within the wings of the aircraft. Furthermore, internal wing space is used efficiently so that internal space elsewhere in the aircraft is not taken-up by fuel. Such fuel tanks generally need to be vented to enable air to flow into and out of the space above the fuel. For example, air is drawn into the tank when fuel is consumed, during descent or jettison or when dispensing fuel in air-to-air refuelling and air passes out of the tank during ascent or receiving fuel during refuelling.
A first known system comprises a series of fuel tanks (typically three) spaced along an aircraft wing, each with a venting pipe individually connected to a surge tank (an overflow tank that prevents unwanted ejection of fuel from the aircraft) located near the tip of the wing. The surge tank is provided with means to permit venting to atmosphere. Each tank is able to vent independently to the surge tank.
The first known system suffers from various problems. For example, it is difficult, owing to space constraints, to incorporate all of the pipe-work into the wingtip. Also, the design requires relatively high fuel tank pressures to be tolerated, because of restrictions, resulting from the vent system design, on the rates of air and fuel flow thus an increase in the strength of the fuel tanks is required, which, in turn, leads to an undesirable increase in mass.
A second known venting system vents all of the fuel tanks through a common venting line. Each tank is directly connected to the common line so that only one vent pipe connects to the surge tank. This reduces the problem associated with the first known system of there being restricted space in the wingtip. The second system, however, presents problems of its own. For example, an overflow from one fuel tank may cause flooding of the common venting line, thus possibly preventing venting of other fuel tanks. An overflowing tank could directly feed into another tank without the overflow being detected, which can cause undesirable uneven weight distribution in one wing compared to another. Furthermore the design also suffers from having to tolerate relatively high fuel tank pressures, thus requiring an increase in the strength of the fuel tanks, and the consequent undesirable increase in weight.